The present invention relates to a semiconductor integrated circuit including a programmable fuse device.
A large-scale integrated circuit including a processor, a memory, a PLL (phase locked loop) circuit and the like, i.e., a so-called “system LSI” has been known. There are many cases where in such a system LSI, a fuse device is used as a simple program device of a memory repair circuit, a PLL tuning circuit or the like.
As a type of known fuse devices to be provided on a semiconductor substrate, a fuse device having a two-layered structure including a polysilicon layer and a silicide layer has been used. In such a fuse device, at least part of a silicide layer is blown by a current flowing during application of a predetermined program voltage and a resistance value is increased. Only a very small change (specifically, a difference of one or two orders of magnitude) in resistance value between non-programmed state and programmed state of the fuse device is observed. Accordingly, a detector used for detecting a state of the fuse device has to have sufficient sensitivity for detecting a relatively small change in a resistance value of the fuse device (see WO97/12401).
To program (blow) a single fuse device shown in the background art, a current of several tens mA is required. Therefore, a large number of fuse devices cannot be programmed together at a time. Practically speaking, fuse devices are programmed in order so that several to several tens of fuse devices are processed at a time.
Moreover, a time required for programming a single fuse device is several hundred μs to several ms. In a known technique, when a current is fed through a fuse device only for a predetermined time, a program process is temporality stopped to judge whether or not the fuse device is programmed. Then, if a resistance value of the fuse device is not increased to reach a predetermined level, the program process is executed again for a certain amount of time.
In the conventional system LSI, the number of fuse devices installed therein is several tens to 100. Therefore, even when a program time is ensured to provide a sufficient margin of a time required for programming each fuse device, the program time hardly affects test costs, so that the test costs are not increased. However, in a recent system LSI, 500 to 1000 fuse devices have to be provided, and thus, if only the same amount of time as that in the known technique is used for programming each fuse device, a program time is increased. This results in increase in test costs.